As a renewable energy resource, the use of solar cell modules is rapidly expanding. One preferred way of manufacturing a solar cell module involves forming a pre-laminate assembly comprising at least 5 structural layers. The solar cell pre-laminates are constructed in the following order starting from the top, or incident layer (that is, the layer first contacted by light) and continuing to the backing (the layer furthest removed from the incident layer): (1) incident layer (typically a glass plate or a thin polymeric film (such as a fluoropolymer or polyester film), but could conceivably be any material that is transparent to sunlight), (2) front encapsulant layer, (3) voltage-generating component (or solar cell component), (4) back encapsulant layer, and (5) backing layer.
The encapsulant layers are designed to encapsulate and protect the fragile voltage-generating component. Generally, a solar cell pre-laminate will incorporate at least two encapsulant layers sandwiched around the solar cell component. The optical properties of the front encapsulant layer must be such that light can be effectively transmitted to the solar cell component.
Until recently, poly(vinyl butyral) (PVB) and ethylene vinyl acetate (EVA) have generally been chosen as the materials for the encapsulant layers. However, none of these encapsulant layer materials encompass all of the end-use requirements. For example, poly(vinyl butyral) compositions often posses high moisture absorption, while ethylene vinyl acetate compositions, on the other hand, suffer the shortcomings of low adhesion to the other components incorporated within the solar cell module, low creep resistance during the lamination process and end-use and low weathering and light stability. These shortcomings have generally been overcome through the formulation of adhesion primers, peroxide curing agents, and thermal and UV stabilizer packages into the compositions, which necessarily complicates the sheet production and ensuing lamination processes.
A more recent development has been the use of higher modulus ethylene copolymers having acid functionality and ionomers derived therefrom in solar cell structures. See, e.g., U.S. Pat. No. 5,476,553; U.S. Pat. No. 5,478,402; U.S. Pat. No. 5,733,382; U.S. Pat. No. 5,741,370; U.S. Pat. No. 5,762,720; U.S. Pat. No. 5,986,203; U.S. Pat. No. 6,114,046; U.S. Pat. No. 6,353,042; U.S. Pat. No. 6,320,116; U.S. Pat. No. 6,690,930; US 2003/0000568; and US 2005/0279401. However, although the ionomer compositions have excellent weatherability and adhesion to other solar cell laminate layers (e.g., glass), they tend to be high modulus and therefore fail to provide adequate shock absorbance.
There is a need to provide tailored encapsulant layers that fulfill all the end-use requirements.